1. Field of the Invention
The present invention relates to a method of processing a substrate such as a semiconductor substrate subjected to an exposure process, a glass substrate for a liquid crystal display device, a glass substrate for a photomask, a substrate for an optical disk and the like, and a substrate processing apparatus for executing the method.
2. Description of the Background Art
As is well known, semiconductor and liquid crystal display products and the like are fabricated by performing a series of processes including cleaning, resist coating, exposure, development, etching, interlayer insulation film formation, heat treatment, dicing and the like on the above-mentioned substrate. An apparatus which performs a resist coating process on a substrate to transfer the substrate to an exposure unit and which receives an exposed substrate from the exposure unit to perform a development process on the exposed substrate, among the above-mentioned processes, is widely used as a so-called coater-and-developer.
The exposure unit (also known as a stepper) for performing an exposure process is typically connected to and provided in juxtaposition with the above-mentioned coater-and-developer, and prints a circuit pattern on a substrate formed with a resist film. With recent decrease in width of lines exposed to light, a lamp for use in printing of a pattern in such an exposure unit is shifting from a conventional ultraviolet light source toward a KrF excimer laser light source and also toward an ArF excimer laser light source. A chemically amplified resist is used when a pattern is printed using a KrF light source and an ArF light source. The chemically amplified resist is a photoresist of the type such that an acid formed by a photochemical reaction during the exposure process acts as a catalyst for resist reactions such as crosslinking, polymerization and the like in the subsequent heat treatment step to change the solubility of the resist in a developing solution, whereby pattern printing is completed.
When the chemically amplified resist is used, a slight variation in processing conditions exerts a large influence upon line width uniformity because an extremely small amount of acid catalyst is formed during the exposure process. In particular, it is known that the time interval between the instant of the end of the exposure process and the instant of the start of a post-exposure bake process exerts the greatest influence on the line width uniformity. Thus, a technique for controlling the time interval between the end of the exposure process and the start of the post-exposure bake process to be constant is proposed, for example, in Japanese Patent Application Laid-Open No. 2002-43208 and Japanese Patent Application Laid-Open No. 2004-342654. Such a technique can improve the line width uniformity when the chemically amplified resist is used.
However, the completely synchronized transfer of substrates has not been conventionally done between the coater-and-developer and the exposure unit. For example, when the exposure unit is about to transfer an exposed substrate to the coater-and-developer, a transfer robot in the coater-and-developer might be able to receive the exposed substrate immediately to transport the exposed substrate to a post-exposure bake processor or be unable to receive the exposed substrate immediately because the transfer robot is performing the operation of transferring an unexposed substrate to the exposure unit. Under these circumstances, it is difficult to control the time interval between the end of the exposure process and the start of the post-exposure bake process as described above to be constant.